This invention relates to an apparatus for providing relief to an operating chamber of a hydraulic unit which is under high pressure. More specifically, the invention relates to such an apparatus for the working chamber of a hydraulic cylinder.
It is known to provide pressure relief (decompression or venting operation) by means of a pilot actuated 2/2 control valve (a so-called poppet valve or logic unit). So as to avoid a relief noise or relief blows, the opening movement of the poppet of the 2/2 control valve has to occur with a speed as low as possible. For that purpose the pilot oil which is used for the actuation of the control poppet of the main or poppet valve is removed from the control chamber of the 2/2 poppet valve via a correspondingly small dimensioned fixed throttle or orifice. This kind of pressure relief requires a relatively long time until the pressure in the working chamber reaches the level of the tank pressure.